Direct-actuated
type HYPER VTEC Reconciling High Revolution and High Power and
Environmental Performance

In sports type motorcycle engines, especially in 4-stroke
engines of medium displacement, the maximum revolution reaches
to a level as high as 13,500rpm. To cope with such high revolution,
Asaka R&D Center has developed a compact and simple "direct-actuated"
type variable valve control system, HYPER VTEC. This is an
epoch-making system as switchover is made from two-valves
to 4-valves per cylinder in the low and medium speed range
and the high speed range is completed in the valve lifter
without using the locker-arms, so the increase of mass is
checked of the kinetic valve system and the ease of operation
is secured in high revolution range.

Points
of HYPER VTEC development

In January 1999, valve control system for 4-stroke
engines, HYPER VTEC, was announced.
It was put on sale, mounting on the new sports bike, CB400
SUPER FOUR.

HYPER VTEC is a valve pausing system, further advancing
VTEC technology through hydraulic control unique of Honda,
in pursuit of the improvement in the suction, exhaust
efficiency and combustion efficiency of 4-cycle engines.
A direct-actuated type is adopted, in which cams will
directly push up the valves through lifters. The system
enabled to switch over the number of valve operations
per cylinder between low and medium speed revolution range
and high speed revolution range, and by setting cam profiles
to give optimum valve timing to the valves on working
side and on paused side, power output characteristics
were demonstrated in the low and medium speed revolution
range and in the high speed revolution range for further
improvement in fuel consumption rate.

Further
Evolution to HYPER VTEC SPEC II and III

HYPER VTEC keeps on evolving, without slackening.

In January 2002, HYPER VTEC evolved into Spec II aiming
at letting everybody actually feel the power drive over
the entire ranges. As one of the aims of Spec II development,
it can be pointed out that the CB400 SUPER FOUR, the model
on which the system was installed, is the one having a
wide user class. There were voices to point out that beginners,
in particular, were unable to fully utilize the four-valve
stage from above the revolution range of 6,700. The development
team then developed HYPER VTEC SPEC II anew to enable
many more users to enjoy the four-valve stage of HYPER
VTEC.
SPEC II achieved increasing torque in the middle speed
range and smoother power by refining the valve timing,
inteke and exhaust systems, and the valve switchover timing
revolution from two to four valves was changed from 6,750rpm
to 6,300rpm. It has resulted in powerful and sporty engines,
enabling one to actually feel VTEC in all driving ranges
from low to top. In December 2003, SPEC III was introduced.
The switchover timing for a 6 speed only was changed from
6,300rpm to 6,750rpm to improve fuel consumption in cruising
over high speed roads without spoiling the cheerful drive.